DIFFRACTIVE DISSOCIATION : THEORIES

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DIFFRACTIVE DISSOCIATION : THEORIES

K. Zalewski

To cite this version:

K. Zalewski. DIFFRACTIVE DISSOCIATION : THEORIES. Journal de Physique Colloques, 1973, 34 (C1), pp.C1-274-C1-276. �10.1051/jphyscol:1973132�. �jpa-00215212�

K. ZALEWSKI

DIFFRACTIVE DISSOCIATION : THEORIES

K. ZALEWSKI

I n s t i t u t e o f Nuclear Research Krakow, Poland

The s u b j e c t of t h i s mini-report i s t h e t h e o r y of e x c l u s i v e , few body d i f f r a c t i o n d i s s o c i a t i o n proces- ses. The p i c t u r e u s u a l l y a p p l i e d by t h e o r i s t s t o d e s c r i b e such p r o c e s s e s i s shown i n Fig.1

The numbers r e f e r t o t h e t h r e e problems i t r a i s e s 1 ) What i s exchanged ?

2 ) What i s produced ? 3 ) What i s t h e c o u p l i n g ?

Before we d i s c u s s t h e s e problems l e t u s mention pro- blem 'b"

0 ) I s t h a t t h e r i g h t p i c t u r e ?

The answer i s " n o t - n e c e s s a r i l y ' ' , i n s p i t e of t h e f a c t t h a t almost a l l q u a n t i t a t i v e work i s based on t h i s p i c t u r e . Among a l t e r n a t i v e p o s s i b i l i t i e s t h e r e i s t h e theory of Cheng and Wu and t h e shadow p i c t u r e advocated r e c e n t l y by BiaYas and Kotanski [ I ]

.

t h e o r y of Cheng and Wu h a s been a l r e a d y reviewed ( c f . e.g. r e f . [ 2 1). The t h e o r y of ~ i a l ' a s and Kotans- k i i s based on t h e assumption t h a t d l f f r a c t i v e d i s -

s o c i a t i o n , j u s t l i k e high-energy e l a s t i c s c a t t e r i n g , i s e s s e n t i a l l y t h e shadow o f o t h e r i n e l a s t i c proces- s e s . T h i s approach g i v e s a number of i n t e r e s t i n g s u g g e s t i o n s , e.g. one f i n d s t h a t t h e d i s t r i b u t i o n of d i f f r a c t i v e l y produced p a r t i c l e s c o n t a i n s both a s c a l i n g and a non-scaling p a r t , which is a v e r y unorthodox answer t o t h e i m p o r t a n t q u e s t i o n whether d i f f r a c t i v e p r o d u c t i o n s c a l e s . A f t e r t h i s warning concerning t h e a p p l i c a b i l i t y of Fig.1 we proceed t o t h e d i s c u s s i o n of t h e t h r e e problems.

1.- WHAT I S EXCHANGED ?.

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r i n g . F o r a d i s c u s s i o n of t h e e x p e r i ~ ~ e m t a l d a t a from t h i s p o i n t o f view c f ref.[3]. Some new d a t a w i l l be p r e s e n t e d by H. L u b a t t i a t t h e p r e s e n t s e s s i o n .

The analogy with e l a s t i c s c a t t e r i n g e x p l a i n s e a s i - l y s e v e r a l f e a t u r e s of d i f f r a c t i v e d i s s o c i a t i o n :

a ) L i t t l e energy dependence b) No quantum number exchange C ) P e r i p h e r a l i t y

d ) Approximately e q u a l c r o s s - s e c t i o n s f o r t h e d i s s o c i a t i o n o f a p a r t i c l e and i t s a n t i - p a r t i c l e

e ) Approximate f a c t o r i s a t i o n

f ) According t o some models [ 1 ] , [ 4 1 , t h e prefe- r e n c e i s f o r d i f f r a c t i v e d i s s o c i a t i o n p r x e s s e s ac- c o r d i n g t o

X

'

,

wher.e X* i s e i t h e r i d e n t i c a l with t h e d i s s o c i a t i n g p a r t i c l e X o r i s a resonance decaying i n t o X +

something. The p r e f e r e n c e f o r p r o c e s s e s of type (1) seems t o be supported by t h e experimental d a t a [ 5 ] . A p o s s i b l y important remark i s t h a t i n d i f f r a c t i v e d i s s o c i a t i o n , a s compared w i t h e l a s t i c s c a t t e r i n g , t h e c o n t r i b u t i o n of Pomeron exchange i s s t r o n g l y reduced. As s t r e s s e d by Kane and o t h e r s ( c f . [ 6 ] and r e f e r e n c e s c o n t a i n e d t h e r e ) i t i s comparable w i t h o t h e r exchanges i n e l a s t i c s c a t t e r i n g . Consepuently Pomeron exchange c a n dominate i n d i f f r a c t i v e d i s s o - c i a t i o n , o n l y i f t h e o t h e r exchanges a r e a l s o redu- ced. I t i s p o s s i b l e t o c o n s t r u c t models 161, where t h i s i s n o t t h e c a s e .

2.- WHAT I S PRODUCED ?.- Here s e v e r a l p o s s i b i l i t i e s have been advocated.

a ) A resonance w i t h coupled decay c h a n n e l s ( i n a n o t h e r language a p o l e screened by a c u t ) [71. The assumption about coupled decay c h a n n e l s i s n e c e s s a r y t o avoid a Breit-Wigner phase, which i s i n c o n s i s t e n t w i t h t h e r e s u l t s of p a r t i a l wave a n a l y s i s of t h e experimental d a t a [7].

b ) A group of p a r t i c 3 e s . T i l l r e c e n t l y t h i s seemed t o be t h e obvious a l t e r n a t i v e t o t h e preceding pos- s i b i l i t y .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1973132

DIFFRACTIVE DISSOCIATION : THEORIES C1-275

c ) A d r o p l e t of h a d r o n i c matter. Some o t h e r names f o r t h i s o b j e c t a r e : f i r e b a l l , c l u s t e r t r u n c a t e d hadron, p a r t i c l e i n s t a t u nascendi. The d r o p l & would r a p i d l y decay i n t o t h e u s u a l p r o d u c t s of d i f f r a c t i v e d i s s o c i a t i o n . T h e r e f o r e i n f o r m a t i o n about i t s pro- p e r t i e s can be e x p e r i m e n t a l l y obtained only from s c a t - t e r i n g on n u c l e i , where t h e d r o p l e t h a s a chance of i n t e r a c t i n g with a nucleon a v e r y s h o r t time a f t e r i t was produced on a n o t h e r nucleon.

D r o p l e t s a s d e s c r i b e d above were f i r s t put forward [ 8 ] i n o r d e r t o i n t e r p r e t t h e s u r p r i s i n g l y low mul- t i p l i c i t y of p a r t i c l e s produced i n t h e i n t e r a c t i o n s ( n o t n e c e s s a r i l y d i f f r a c t i v e ) of high energy cosmic r a y s with n u c l e i . Now t h e i d e a i s r a p i d l y g a i n i n g s u p p o r t [41 and [9-131

.

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3.- WHAT I S THE COUPLING ?.

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however, we w i l l d i s c u s s o n l y t h e s o c a l l e d Deck mechanism. Deck [ 1 6 1 i n t e r p r e t e d a s shown i n Fig.2 t h e p i c t u r e Fig.1

I t was soon suggested t h a t t h e diagrams shown i n f i g u r e 3 should be a l s o i n c l u d e d

Cf. [17] f o r t h e e a r l y h i s t o r y of t h e model, [IS]

f o r a r e c e n t d i s c u s s i o n and [19] f o r a somewhat d i f - f e r e n t , b u t comparable approach, which i n c l u d e s t h e simultaneous i n t e r a c t i o n of Y w i t h X* and 'K

.

The two diagrams f i e u s e 3 c o n t r i b u t e w i t h o p p o s i t e s i g n , and a r e n e g l e c t e d i n t h e hope t h a t they c a n c e l . I n some c a s e s ( i n p a r t t c u l a r f o r X = ^{X) t h i s i s f a r}

from obvious.

The Deck mechanism e x p l a i n s e a s i l y s e v e r a l f e a t u r e s of d i f f r a c t i v e d i s s o c i a t i o n :

a ) The p r e f e r e n c e f o r d i s s o c i a t i o n s X ^{-t X*X} b) The dominance o f low (x*X) masses

C ) The dominance o f t h e l o w e s t p o s s i b l e a n g u l a r momentum i n t h e X*X system

d) Approximate t-channel h e l i c i t y c o n s e r v a t i o n ( c f . r e f . [20] and r e f e r e n c e s c o n t a i n e d t h e r e ) .

According t o a paper s u b m i t t e d t o t h e p r e s e n t con- f e r e n c e [211

,

A q u a n t i t a t i v e d i s c u s s i o n t a k i n g i n t o account t h a t B(1235) i s n o t q u i t e exchange d e g e n e r a t e w i t h t h e X h a s n o t y e t been given, b u t t h e q u a l i t a t i v e p r e d i c - t i o n s a g r e e w i t h experiment.

I n s p i t e of t h e s e s u c c e s s e s a s e r i o u s d i f f i c u l t y of t h e Deck model, and of t h e r e l a t e d models i n c l u - d i n g t h e d u a l ones [221,[231, h a s been p o i n t e d o u t i n r e f . [24]

.

where A i s a n o t h e r tl - independent parameter.

C1-276 K. ZALEWSKI

According t o Deck type models t h e r e should be l i t t l e dependence of b on M

.

I t would be i n t e r e s t i n g t o r e p e a t t h e a n a l y s i s from r e f . [24] f o r experiments w i t h h i g h e r s t a t i s t i c s and/

o r o t h e r d i f f r a c t i v e channels. I f t h e r e s u l t from r e f . [241 is confirmed, t h e Deck type models o f d i f - f r a c t i v e d i s s o c i a t i o n w i l l be au.t. Note i n c i d e n t a l l y

t h a t such models a r e p l a u s i b l e only i f X d i s s o - c i a t e s d i r e c t l y i n t o X*X w i t h o u t a d r o p l e t o r r e - sonance i n t e r m e d i a t e s t a t e .

REMERCIEMENTS. - The a u t h o r thanks D r s . E. BERGER, A. BIAYAS, G. COHEN-TANNOUDJI, J.T. DONOHUE, J.D.

DORREN, E. FEINBERG, A. KRZYWICKI.,H. LUBATTI and H. SATZ f o r d i s c u s s i o n s o n v a r i o u s a s p e c t s of d i f -

f r a c t i v e d i s s o c i a t i o n .

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